Poly(arylene ether) resins are a class of plastics known for excellent water resistance, dimensional stability, and inherent flame retardancy, as well as high oxygen permeability and oxygen/nitrogen selectivity. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending poly(arylene ether) resins with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and insulation for wire and cable. The poly(arylene ether) most commonly used and widely commercially available is poly(2,6-dimethyl-1,4-phenylene ether).
Various odorous impurities that may be present in poly(arylene ether) resins have discouraged its adoption for odor-sensitive applications such as the molding of containers for food, cosmetics, and pharmaceuticals. One source of odors in poly(arylene ether) resins is di-n-butylamine, which is used as a component of the polymerization catalyst employed by the two largest manufacturers of poly(2,6-dimethyl-1,4-phenylene ether). The resulting poly(2,6-dimethyl-1,4-phenylene ether) resins can exhibit a di-n-butylamine-related odor from free di-n-butylamine impurities in the poly(2,6-dimethyl-1,4-phenylene ether). On the other hand, di-n-butylamine is also incorporated into the poly(2,6-dimethyl-1,4-phenylene ether) molecule as di-n-butylamino substituents, the thermal decomposition of which can provide a beneficial increase in poly(2,6-dimethyl-1,4-phenylene ether) molecular weight during compounding, as well as improved compatibilization of poly(2,6-dimethyl-1,4-phenylene ether) with incompatible resins such as polyamides.
One approach to reducing the odor of poly(2,6-dimethyl-1,4-phenylene ether) resins has been to utilize polymerization catalysts with less odorous amines. For example, proton nuclear magnetic resonance spectroscopy (1H NMR) analysis of a poly(2,6-dimethyl-1,4-phenylene ether) obtained in China from Bluestar New Chemical Materials Co., Ruicheng Branch, China, indicates the presence of morpholino substituents and the absence of di-n-butylamino substituents. This analysis suggests that these poly(2,6-dimethyl-1,4-phenylene ether) resins are synthesized using a polymerization catalyst comprising morpholine rather than di-n-butylamine. Although the poly(2,6-dimethyl-1,4-phenylene ether) resins synthesized with a morpholine-containing catalyst exhibit reduced odor, they also exhibit undesirable reductions in their molecular weight increase during compounding and their compatibilization with resins such as polyamides. Thus, there remains a need for a poly(2,6-dimethyl-1,4-phenylene ether) which is synthesized without di-n-butylamine but which exhibits the molecular weight gain and compatibilization advantages of poly(2,6-dimethyl-1,4-phenylene ether) resins synthesized with di-n-butylamine.